1. Field of the Invention
This invention relates generally to material handling systems, and more particularly, to a novel axle construction for portable radial stackers.
2. Description of the Prior Art
Conveyor systems and devices used to stack or pile material are well known in the art. These devices utilize various principles of the conveying art, including augers, conveyor belts, buckets and similar conveying means. The material may be moved intermittently or may be moved continuously to a stockpile and in fact, may include movement in the vertical, horizontal or inclined directions.
One of the specific applications for the conveyor system is to stockpile loose bulk material including such material as earth, coal, sand, ore, grain. These materials are generally stockpiled by using a conveyor system which transports the material from the material loading position at an angle inclined upwards and then the material is dropped off the end of the conveyor (the material unloading position). As this material is loose material, it will form a conical-shaped pile of its own accord.
More recently, in order to minimize the area necessary to stockpile this loose material, radial stackers have been used. Radial stackers are conveyor systems wherein the terminal end can pivot in an arc around the point where the material is loaded onto the conveyor. Thus, the material is stockpiled in an arc thereby allowing much more of the material to be stockpiled within a specified area than would be stacked if separate piles were used.
Recently, radial stackers have been designed to be portable, that is, designed to be able to be transported from one location to another. These devices are attached to the rear of a truck or other transporting vehicle and are towed from one location to another. A supporting means is provided which, in addition to supporting the stacker at the desired angle during use, provides a set of wheels upon which the rear portion of the stacker is supported during transporting. This has removed the necessity of placing the stacker on a bed during transportation and has increased the utility of the stacker tremendously.
Many of these constructions utilize telescopic axles to allow the stacker to lie flat during transport but they suffer from the disadvantage that the load concentration point during stacking and the carrying concentration point during transporting are the same. This is, the concentration point of the axle during both the loading stage and the transportation stage is located at the balance point of the conveyor. Thus, when the stacker is transported, uplifting will occur at the fifth wheel pin of the truck creating an unstable and dangerous condition. This is particularly prevalent when the stacker is transported over rough roads and terrain. The impact impulses which are caused by the rough road creates a lifting action at the fifth wheel pin of the truck which will cause breakage and is very hazardous.
It has been proposed to reduce this uplifting effect by moving the wheels of the stacker more towards the rear. However, this will decrease the stockpiling capacity of the stacker for two essential reasons. If the wheels are moved rearward, the material which is stockpiled will bury the wheels if the same angle of inclination is used for the stacker. If the angle is raised, more elaborate machinery is necessary and the wheels of the stacker will still be buried during use.
If the wheels of the support means of the stacker are moved forward towards the front of the stacker to increase the stockpiling capacity, this creates very hazardous road conditions during transporting the stacker as the uplifting of the fifth wheel pin on the truck is increased. It is possible to reinforce the fifth wheel pin on the transporting vehicle however this increases the costs substantially and decreases the safety factor during transportation of the stacker.
The effect of the impact impulses caused by the road conditions during the transporting of the stackers is a very serious problem. Some of the impulses may be absorbed by the tires themselves but it has been found with the devices presently in use that the tires manufactured today cannot absorb all the impulses created by the road conditions during the transportation of these stackers. Blow-outs of the tires are very common and irreperable damage is done to the tires. The average weight of one of these stackers is 20,000 lbs. thus putting a load of about 10,000 lbs. per tire. Very heavy tires with sufficient reinforcements are required to prevent these blow-outs which is not satisfactory from a design or cost aspect.
It has also been suggested that two tires may be used to increase the safety factor during transportation of these stackers. However, if two tires are used with the devices of the prior art, when the stacker is put into the operating position, only one tire will be on the ground and the weight is not distributed equally. A further drawback to using two tires is the accompanying increase in the width of the stacker. Most jurisdictions placed a maximum of 12 feet for the width of a vehicle on the roads. The use of a double tire will increase the width of many stackers beyond this legal limit and thus prevent them from being transported on public roads.